For more than half a century, the cathode ray tube (CRT) has been the principal device for electronically displaying visual information. Although CRTs have been endowed during that period with remarkable display characteristics in the areas of color, brightness, contrast and resolution, they have remained relatively bulky and power hungry. The advent of portable computers has created intense demand for displays which are lightweight, compact, and power efficient. Liquid crystal displays (LCDs) are now used almost universally for lap-top computers. However, contrast is poor in comparison to CRTs, only a limited range of viewing angles is possible, and battery life is still measured in hours rather than days.
As a result of the drawbacks of LCD and CRT technology, field emission display (FED) technology has been receiving increased attention by industry. Flat panel displays utilizing FED technology employ a matrix-addressable array of cold, pointed field emission cathodes in combination with a luminescent phosphor screen. Somewhat analogous to a cathode ray tube, individual field emission structures are sometimes referred to as vacuum microelectronic triodes. Each triode has the following elements: a cathode (emitter tip), a grid (also referred to as the gate), and an anode (typically, the phosphor-coated element to which emitted electrons are directed).
FIG. 1 illustrates a cross-sectional view of a prior art field emission display device 10. Device 10 comprises a face plate 12, a base plate 14, and spacers 26 extending between base plate 14 and face plate 12 to maintain face plate 12 in spaced relation relative to base plate 14. Face plate 12, base plate 14 and spacers 26 can comprise, for example, glass. Phosphor regions 16, 18 and 20 are associated with face plate 12, and separated from face plate 12 by a transparent conductive layer 22. Transparent conductive layer 22 can comprise, for example, indium tin oxide or tin oxide. Phosphor regions 16, 18 and 20 comprise phosphor-containing masses. Each of phosphor regions 16, 18 and 20 can comprise a different color phosphor. Typically, phosphor regions 16, 18 and 20 comprise either red, green or blue phosphor. A black matrix material 24 is provided to separate phosphor regions 16, 18 and 20 from one another.
Base plate 14 has emitter regions 36, 38 and 40 associated therewith. The emitter regions comprise emitters 42 which are located within radially symmetrical apertures 44 (only some of which are labeled) formed through a conductive gate layer 46 and a lower insulating layer 48. Emitters 42 are typically about 1 micron high, and are separated from base 14 by a conductive layer 50. Emitters 42 and apertures 44 are connected with circuitry (not shown) enabling column and row addressing of the emitters 42 and apertures 44, respectively.
A voltage source 60 is provided to apply a voltage differential between emitters 42 and surrounding gate apertures 46. Application of such voltage differential causes electron streams 61, 62 and 63 to be emitted toward phosphor regions 16, 18 and 20, respectively. Conductive layer 22 is charged to a potential higher than that applied to gate layer 46, and thus functions as an anode toward which the emitted electrons accelerate. Once the emitted electrons contact phosphor dots associated with regions 16, 18 and 20, light is emitted. As discussed above, the emitters 42 are typically matrix addressable via circuitry. Emitters 42 can thus be selectively activated to display a desired image on the phosphor-coated screen of face plate 12.
Typical phosphor arrangements associated with a face plate 12 are shown in FIGS. 2 and 3. Specifically, FIGS. 2 and 3 illustrate alternative embodiment face plates 12, with the face plates having red, green and blue phosphor regions (illustrated as regions labeled "R", "G", and "B", respectively), and black matrix areas 24 surrounding the phosphor regions. Also, the face plates have locations wherein spacers 26 are bound. The face plate of FIG. 2 corresponds to a display using Sony Trinitron.RTM. scanning, and the face plate construction of FIG. 3 corresponds to a phosphor/black matrix pattern of a conventionally-scanned color display.
The three phosphor colors (red, green, and blue) can be utilized to generate a wide array of screen colors by simultaneously stimulating one or more of the red, green and blue regions. The simultaneous stimulation of multiple regions generates a blend of colors. However, if the color blend is inaccurate, an incorrect color will be displayed. Also, an inaccurate color blend can cause a dirty, non-uniform appearance of a displayed image (a so-called "muddying" of the appearance of a displayed image). Inaccurate color blending can result from, for example, lost illumination efficiency. Illumination efficiency is a measure of the amount of light passed through face plate 12 and toward a viewer relative to the amount of electrons striking a phosphor region. Illumination efficiency is decreased if electrons strike a phosphor region and cause something other than light passing through face plate 12. For the above-discussed reasons, it would be desirable to develop methods and apparatuses which improve illumination efficiency and enhance blending of primary phosphor colors.